1. Field of the Invention
The teachings herein relate to geophysical exploration, and in particular, to use of conducting polymers in such exploration.
2. Description of the Related Art
A large variety of tools, instruments and techniques are used for geophysical exploration. A number of these make use of electronic components to achieve a desired result. As is known in the art, the tools and instruments are inserted into a borehole (also referred to as a “wellbore”) which has been drilled into subterranean formations of interest.
The downhole environment typically presents harsh conditions for electromagnetic equipment, thereby affecting electromagnetic properties of the equipment. For example, elevated downhole temperatures can not only change electrical conductivities of the equipment, but the temperatures can also damage the equipment, such as by melting solder joints present on printed circuit board (PCBs).
New materials are coming available for use in electrical and electronic systems. For example, consider conductive polymers. A conductive polymer is referred to typically as an organic polymer semiconductor, or an organic semiconductor. Roughly, there are two classes: charge transfer complexes and conductive polyacetylenes. The latter include polyacetylene itself as well as polypyrrole, polyaniline, and their derivatives. Other embodiments of conductive polymers are known.
Most commercially produced organic polymers are electrical insulators. Conductive organic polymers often have extended delocalized bonds (often composed of aromatic units). At least locally, these create a band structure similar to silicon, but with localized states. When charge carriers (from the addition or removal of electrons) are introduced into the conduction or valence bands (see below) the electrical conductivity increases dramatically. Technically almost all known conductive polymers are semiconductors due to the band structure and low electronic mobility. However, so-called zero band gap conductive polymers may behave like metals. The most notable difference between conductive polymers and inorganic semiconductors is the mobility, which until very recently was dramatically lower in conductive polymers than their inorganic counterparts, though recent advancements in molecular self-assembly are closing that gap.
Delocalization can be accomplished by forming a conjugated backbone of continuous overlapping orbitals. For example, alternating single and double carbon-carbon bonds can form a continuous path of overlapping p-orbitals. In polyacetylene, but not in most other conductive polymers, this creates degeneracy in the frontier molecular orbitals. This leads to the filled (electron containing) and unfilled bands (valence and conduction bands respectively) resulting in a semiconductor.
Conductive polymers are also referred to in the art as “Inherently Conducting Polymers,” and “Intrinsically Conducting Polymers,” (ICP's).
What are needed are improved electronic and electrical components for use in downhole environments. Preferably, these components take advantage of advances in conductive polymers.